You can ensure understanding by attaching a survey to your Policy.
When creating a Survey, select the Create as Attached Survey checkbox. (This will make your Survey available to add to your Policy upon publication.)
When a Survey has been added to your Policy, users will not be able to 'Accept the Policy' until they have achieved the required pass mark.
You can also select the Enable Time Spent checkbox when publishing your policy. (This allows you to view, within the 'Audit Reports', the time each user has spent viewing the Policy.)